Many articles that previously have been formed from lead are now formed from other materials because of health concerns regarding the toxicity of lead. Examples of materials that have proven effective as lead substitutes are materials that are formed from tungsten and/or tungsten alloys. One significant factor why tungsten and its alloys are effective for use as lead substitutes is that tungsten is very dense. More specifically, tungsten has a density of 19.3 g/cc, which is significantly higher than that of lead, which has a density of 11.3 g/cc. Many tungsten alloys also have densities that are greater than, and often much greater than, the density of lead, with many tungsten alloys having a density greater than 15 g/cc. By having such a high density, tungsten and its alloys can be mixed with other metal, polymer, or other materials to form a composite material that still has a sufficient density to be used as a lead substitute, such as a density that equals that of lead, that is greater than that of lead, that is near the density of lead, etc.
In many applications, tungsten-containing materials are utilized in powder metallurgy applications. As such, these powder-form materials may be referred to as tungsten-containing powders. These powders may be utilized alone, although they are often mixed with other materials, such as one or more binders, lubricants and the like. During formation of these articles via powder metallurgy, factors to be considered are the strength and density of the article, as well as the flowability of the tungsten-containing powder used to form the article. For example, if a particular powder blend produces sufficiently dense and strong articles, it still may not be commercially viable if the powder used to form the articles does not readily flow and therefore cannot be effectively distributed in an automated or other mechanized (typically large scale) manufacturing process. Similarly, a tungsten-containing powder that flows sufficiently well to be used in mechanized (preferably larger scale) processes, but which does not yield sufficiently dense or strong articles also is not commercially viable.
Another consideration is the availability of the tungsten-containing material. For example, if a particular material performs well, such as in the criteria described above, but is very scarce and/or prohibitively expensive compared to other available materials, then this material may not be a commercially viable lead substitute simply because it cannot be obtained in sufficient quantities for larger scale manufacturing processes and/or obtained in sufficient quantities at a commercially acceptable price. Therefore, it is desirable for a tungsten-containing material that will be used as a lead substitute to be at least substantially formed from a material that is reliably commercially available in larger quantities at consistent quality levels and relatively stable prices. As an aspect of this factor, for some materials, the effectiveness of the material for powder metallurgical processes varies, sometimes dramatically, depending upon the particle size of the material being utilized. Therefore, the availability and economics of obtaining a desired tungsten-containing material in a desired form needs to be considered.
One type of tungsten alloy is ferrotungsten, which is an alloy of tungsten and iron. Ferrotungsten is commercially available as a commodity product, with the largest present application of ferrotungsten being a feedstock component for many steels such as steels used to make high-speed cutting tools. Conventionally, ferrotungsten is utilized by the steel industry with consideration essentially only being given to the weight percentage (wt %) of tungsten in the ferrotungsten. In other industries, such as the firearms industry, tungsten, ferrotungsten, and other tungsten alloys are being used to form non-toxic firearms projectiles, such as via powder metallurgy and melt and cast/quench techniques. Conventionally, consideration is given to the bulk density of ferrotungsten, namely, the theoretical and actual density of articles produced from ferrotungsten, with the theoretical density being calculated based on the overall weight percentage of ferrotungsten in the article being produced.